Make or prepare the pie dough: If making from scratch, chill your two discs of dough for at least 1 hour. Keep them cold until rolling.

Preheat and prep: Place a rimmed baking sheet on the middle rack and preheat the oven to 425°F (220°C). The hot sheet helps crisp the bottom crust.

Mix the filling: In a large bowl, combine blueberries, sugar, cornstarch, lemon zest, lemon juice, cinnamon, and a pinch of salt. Toss gently until the berries are evenly coated. Let sit 5 minutes to start releasing juices.

Roll the bottom crust: On a lightly floured surface, roll one disc to about 12 inches. Fit it into a 9-inch pie plate, letting the excess hang over the edge. Chill while you roll the top.

Fill the pie: Spoon the blueberry mixture into the crust. Dot the top with small pieces of butter.

Add the top crust: Roll the second disc to about 12 inches. Lay it over the filling, or cut into strips for a lattice. Trim excess, leaving about 1 inch overhang. Fold and crimp to seal.

Vent and brush: If using a full top crust, cut 4–5 small slits for steam. Whisk the egg with 1 teaspoon water and brush the top. Sprinkle with coarse sugar if you like.

Chill the assembled pie: Place the pie in the fridge or freezer for 15–20 minutes. Cold dough equals flakier crust and better shape.

Bake hot, then lower: Set the pie on the preheated baking sheet. Bake at 425°F (220°C) for 20 minutes. Reduce heat to 375°F (190°C) and bake another 35–45 minutes, until the crust is deep golden and the filling is bubbling in the center.

Cool completely: Transfer to a rack and cool at least 3–4 hours. This lets the filling set so slices hold together.

Serve: Slice with a sharp knife. Serve as is or with vanilla ice cream or whipped cream.